Hoists for hoisting loads by means of a cable have long existed. Generally, the principle of operation of a hoist is based on the cable being driven by adherence of the cable to the drum of the hoist. The drum holds the cable by friction, which operates as the principal power means for drawing in the cable for winding around the drum. As tension that is applied to the cable increases, the cable stretches and its linear speed decreases accordingly.
There are various types of hoists, which include winches and capstans. A winch is used to wind up a cable in which one end of the cable is fixed and the cable is generally stored on the drum of the winch. Besides industrial applications, for example on lifting cranes, winches are also used on vehicles for towing cars and boats. Winches are widely used for hoisting loads as they provide mechanical advantage to users. However, a drawback of using a winch to hoist a load is that sufficient tension must be constantly maintained on the turns for the cable to be suitably wound and stored on the drum. Typically, a guide mechanism is used for progressively guiding the cable across the length of the drum as the cable is being wound onto the drum.
Capstans are similar to winches with the exception that the cable is not stored on the drums. Hence, capstans do not have the problem of constantly maintaining sufficient tension on the turns for the cable to be suitably wound and stored on the drums. Capstans are rotating machines used to apply force to another element and are typically used on board ships and on dock walls for heaving or veering ropes, cables and hawsers. When a capstan is in operation, only a portion of the cable is wound around the drum of the capstan. A load can be attached to one of the free ends for the capstan to hoist the load. However, as the cable is driven by adherence of the cable to the drum of the capstan, sufficient frictional force is needed between the cable and the drum for operation of the capstan.
Japanese Patent Application Number 20040163404 to Fumiaki discloses an endless type winch having a configuration capable of towing and driving a winch without winding a rope by utilising a part around a driving mechanism of an existing winch as it is. The endless type winch comprises a winding drum having a rope channel at the outer periphery, a pair of rope gripping guide sheaves and a supporting frame. The pair of rope gripping guide sheaves is arranged in positions where the rope winds around the rope channel of the winding drum so as to increase contact frictional force of the rope for the rope channel. However, as the rope elastically contracts due to its tension diminishing in passing through the endless type winch, the length of the rope changes continuously. The rope slides against the rope channel of the winding drum for accommodating the changing rope length, which results in wear and tear of the rope. Further, the sliding of the rope against the rope channel increases slippage of the rope between the drum and the rope gripping guide sheave.
Therefore, there is a need for a hoist, which addresses at least one of the aforementioned problems.